Nested identical filters are not rendered.

mattwoodrow · mattwoodrow · commit c887d10d6123 · 2025-12-09T00:09:56.000-08:00
https://bugs.webkit.org/show_bug.cgi?id=302900 rdar://165163823 Reviewed by Simon Fraser. Pushing a transparency layer causes any current filter style (or shadow, or composite operation) to be applied to the layer when popped, and don't apply to the content in the layer. Make sure we clear those states from the GraphicsContext tracking, to match the behaviour of what CG is doing. If they're not cleared, then a nested filter (or second filter primitive of the same filter property) that is identical is incorrectly considered a no-op, and doesn't get forwarded to the platform code. Test: css3/filters/nested-identical-filters.html * LayoutTests/css3/filters/nested-identical-filters-expected.html: Added. * LayoutTests/css3/filters/nested-identical-filters.html: Added. * Source/WebCore/platform/graphics/GraphicsContextState.cpp: (WebCore::GraphicsContextState::repurpose): Canonical link: https://commits.webkit.org/304143@main
diff --git a/LayoutTests/css3/filters/nested-identical-filters-expected.html b/LayoutTests/css3/filters/nested-identical-filters-expected.html
@@ -0,0 +1,17 @@
+<!doctype HTML>
+<html>
+<head>
+<style>
+  div {
+    position: relative;
+    width: 200px;
+    height: 200px;
+    background: green;
+  }
+</style>
+</head>
+<body>
+  <div>
+  </div>
+</body>
+</html>
diff --git a/LayoutTests/css3/filters/nested-identical-filters.html b/LayoutTests/css3/filters/nested-identical-filters.html
@@ -0,0 +1,22 @@
+<!doctype HTML>
+<html>
+<head>
+<style>
+  div {
+    position: relative;
+    width: 200px;
+    height: 200px;
+    filter: invert(100%);
+  }
+  #inner {
+    background: green;
+  }
+</style>
+</head>
+<body>
+  <div id=outer>
+    <div id=inner>
+    </div>
+  </div>
+</body>
+</html>
diff --git a/Source/WebCore/platform/graphics/GraphicsContextState.cpp b/Source/WebCore/platform/graphics/GraphicsContextState.cpp
@@ -44,8 +44,12 @@ void GraphicsContextState::repurpose(Purpose purpose)
 
 #if USE(CG)
     // CGContextBeginTransparencyLayer() sets the CG global alpha to 1. Keep the clone's alpha in sync.
-    if (purpose == Purpose::TransparencyLayer)
+    if (purpose == Purpose::TransparencyLayer) {
         m_alpha = 1;
+        m_style = std::nullopt;
+        m_dropShadow = std::nullopt;
+        m_compositeMode = { CompositeOperator::SourceOver, BlendMode::Normal };
+    }
 #endif
 
     m_purpose = purpose;
